One of the myriad details required to inspect the critical structures of a nuclear reactor station calls for the internal and external surface cleaning and subsequent inspection of these surfaces of the massive studs mounted in the edge of the wall of the upper opening of the reactor vessel. Dull and prosaic as the task appears, the Gargantuan studs, threaded into their holes at the upper lip of the nuclear reactor vessel, must be unthreaded and subjected to cleaning and inspection. The inspections are a requirement of the ASME Code Section XI and cleaning is necessary prior to this inspection being performed.
It is interesting to recall that in the original installation of these studs, they are literally stretched by massive hydraulic lifting mechanisms attached to the upper ends, while thir nuts are threaded into place and bear upon the cover of the nuclear reactor vessel. A suitable configuration is formed on the upper end of each stud with which the hydraulic stretching mechanism is attached to the stud to exert its upward force. It is the threads for engaging the nut and the threads for engaging the vessel, and the shaft region between these threads, which are the primary targets for cleaning and inspection of the outside surface of the body of the stud. Additionally, there is a bore extending axially up into the stud which it is also important to clean and inspect. When it is considered that each stud has an imposing weight in the order of 1,000 pounds, and length in the order of 6 feet, reality strikes that the cleaner and inspector has an impressive responsibility.
There is need for a support framework on which each stud can be supported to automate large sections of the cleaning and inspection operations. There is a need to automate a reasonable amount of the cleaning and inspection to shorten the time and elevate the quality of these operations, and reduce associated radiation exposure to inspection personnel. With the fact that the debris cleaned from the stud may well have a significant level of radiation contamination, a system for collecting and isolating the material cleaned from the stud must be provided. All of the foregoing bases must be touched competently in order to produce a stud suitable for reinstallation in the nuclear reactor vessel for incorporation in the structure which maintains the vessel closure safely installed on the reactor vessel.